From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2D76BC25B67 for ; Fri, 27 Oct 2023 11:11:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qwKjN-0006tX-5y; Fri, 27 Oct 2023 07:10:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qwKjK-0006sN-Ci; Fri, 27 Oct 2023 07:10:18 -0400 Received: from apollo.dupie.be ([2001:bc8:3f2a:101::1]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qwKjG-0003GO-Iu; Fri, 27 Oct 2023 07:10:18 -0400 Received: from [IPV6:2a02:a03f:eaf7:ff01:ecd9:958e:7098:f62b] (unknown [IPv6:2a02:a03f:eaf7:ff01:ecd9:958e:7098:f62b]) by apollo.dupie.be (Postfix) with ESMTPSA id 7288D1520E7F; Fri, 27 Oct 2023 13:10:08 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dupond.be; s=dkim; t=1698405008; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Wu0AmSpliDQL0jXaBdDIXXbEuRFwuYt2HnhOUwg3eCk=; b=j5i7afV6QjSOCjOXY7/uBeQkjap+kbDqozz/zuHMd+0by2q3c3QFwGvkGhK3OsQh+TJCgX O/pjbU/rfHigbCB0G1fe8kkXlca0aoltpNAffRNl06R7NMzJuC21p5rVXla818K1GpNekY 2CYet4u3I9ZOo/iXXghfEeLA7N3C6zF9QqojD/8VNeJTvWwz2zXVq3eYdsV05rV3WScF6j FAiZLs1NbbKpCuzJEP14jHUatYorgbnj0DgpvkBtjGvuBpG6GP95ycFIidWK3iRX2FZtGT jYqya8jzY20M1rQnHegmdis1/N1PMUcM4b/dG/7gwCAgDpGpstMrfxNsY2UMaQ== Message-ID: Date: Fri, 27 Oct 2023 13:10:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/7] qcow2: make subclusters discardable Content-Language: en-US To: Andrey Drobyshev , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, hreitz@redhat.com, kwolf@redhat.com, eblake@redhat.com, berto@igalia.com, den@virtuozzo.com References: <20231020215622.789260-1-andrey.drobyshev@virtuozzo.com> <20231020215622.789260-5-andrey.drobyshev@virtuozzo.com> From: Jean-Louis Dupond In-Reply-To: <20231020215622.789260-5-andrey.drobyshev@virtuozzo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2001:bc8:3f2a:101::1; envelope-from=jean-louis@dupond.be; helo=apollo.dupie.be X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 20/10/2023 23:56, Andrey Drobyshev wrote: > This commit makes the discard operation work on the subcluster level > rather than cluster level. It introduces discard_l2_subclusters() > function and makes use of it in qcow2 discard implementation, much like > it's done with zero_in_l2_slice() / zero_l2_subclusters(). It also > changes the qcow2 driver pdiscard_alignment to subcluster_size. That > way subcluster-aligned discards lead to actual fallocate(PUNCH_HOLE) > operation and free host disk space. > > This feature will let us gain additional disk space on guest > TRIM/discard requests, especially when using large enough clusters > (1M, 2M) with subclusters enabled. > > Signed-off-by: Andrey Drobyshev > --- > block/qcow2-cluster.c | 100 ++++++++++++++++++++++++++++++++++++++++-- > block/qcow2.c | 8 ++-- > 2 files changed, 101 insertions(+), 7 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index 7c6fa5524c..cf40f2dc12 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -2042,6 +2042,74 @@ discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, uint64_t nb_clusters, > return nb_clusters; > } > > +static int coroutine_fn GRAPH_RDLOCK > +discard_l2_subclusters(BlockDriverState *bs, uint64_t offset, > + uint64_t nb_subclusters, > + enum qcow2_discard_type type, > + bool full_discard, > + SubClusterRangeInfo *pscri) > +{ > + BDRVQcow2State *s = bs->opaque; > + uint64_t new_l2_bitmap, l2_bitmap_mask; > + int ret, sc = offset_to_sc_index(s, offset); > + SubClusterRangeInfo scri = { 0 }; > + > + if (!pscri) { > + ret = get_sc_range_info(bs, offset, nb_subclusters, &scri); > + if (ret < 0) { > + goto out; > + } > + } else { > + scri = *pscri; > + } > + > + l2_bitmap_mask = QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); > + new_l2_bitmap = scri.l2_bitmap; > + new_l2_bitmap &= ~l2_bitmap_mask; > + > + /* > + * If there're no allocated subclusters left, we might as well discard > + * the entire cluster. That way we'd also update the refcount table. > + */ > + if (!(new_l2_bitmap & QCOW_L2_BITMAP_ALL_ALLOC)) { > + return discard_in_l2_slice(bs, > + QEMU_ALIGN_DOWN(offset, s->cluster_size), > + 1, type, full_discard); > + } > + > + /* > + * Full discard means we fall through to the backing file, thus we only > + * need to mark the subclusters as deallocated. > + * > + * Non-full discard means subclusters should be explicitly marked as > + * zeroes. In this case QCOW2 specification requires the corresponding > + * allocation status bits to be unset as well. If the subclusters are > + * deallocated in the first place and there's no backing, the operation > + * can be skipped. > + */ > + if (!full_discard && > + (bs->backing || scri.l2_bitmap & l2_bitmap_mask)) { > + new_l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); > + } > + > + if (scri.l2_bitmap != new_l2_bitmap) { > + set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap); > + qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice); > + } > + > + if (s->discard_passthrough[type]) { > + qcow2_queue_discard(bs, (scri.l2_entry & L2E_OFFSET_MASK) + > + offset_into_cluster(s, offset), > + nb_subclusters * s->subcluster_size); > + } > + > + ret = 0; > +out: > + qcow2_cache_put(s->l2_table_cache, (void **) &scri.l2_slice); > + > + return ret; > +} > + > int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset, > uint64_t bytes, enum qcow2_discard_type type, > bool full_discard) > @@ -2049,19 +2117,36 @@ int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset, > BDRVQcow2State *s = bs->opaque; > uint64_t end_offset = offset + bytes; > uint64_t nb_clusters; > + unsigned head, tail; > int64_t cleared; > int ret; > > /* Caller must pass aligned values, except at image end */ > - assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); > - assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) || > + assert(QEMU_IS_ALIGNED(offset, s->subcluster_size)); > + assert(QEMU_IS_ALIGNED(end_offset, s->subcluster_size) || > end_offset == bs->total_sectors << BDRV_SECTOR_BITS); > > - nb_clusters = size_to_clusters(s, bytes); > + head = MIN(end_offset, ROUND_UP(offset, s->cluster_size)) - offset; > + offset += head; > + > + tail = (end_offset >= bs->total_sectors << BDRV_SECTOR_BITS) ? 0 : > + end_offset - MAX(offset, start_of_cluster(s, end_offset)); > + end_offset -= tail; > > s->cache_discards = true; > > + if (head) { > + ret = discard_l2_subclusters(bs, offset - head, > + size_to_subclusters(s, head), type, > + full_discard, NULL); > + if (ret < 0) { > + goto fail; > + } > + } > + > /* Each L2 slice is handled by its own loop iteration */ > + nb_clusters = size_to_clusters(s, end_offset - offset); > + > while (nb_clusters > 0) { > cleared = discard_in_l2_slice(bs, offset, nb_clusters, type, > full_discard); > @@ -2074,6 +2159,15 @@ int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset, > offset += (cleared * s->cluster_size); > } > > + if (tail) { > + ret = discard_l2_subclusters(bs, end_offset, > + size_to_subclusters(s, tail), type, > + full_discard, NULL); > + if (ret < 0) { > + goto fail; > + } > + } > + > ret = 0; > fail: > s->cache_discards = false; > diff --git a/block/qcow2.c b/block/qcow2.c > index aa01d9e7b5..66961fa59e 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -1966,7 +1966,7 @@ static void qcow2_refresh_limits(BlockDriverState *bs, Error **errp) > bs->bl.request_alignment = qcrypto_block_get_sector_size(s->crypto); > } > bs->bl.pwrite_zeroes_alignment = s->subcluster_size; > - bs->bl.pdiscard_alignment = s->cluster_size; > + bs->bl.pdiscard_alignment = s->subcluster_size; > } > > static int GRAPH_UNLOCKED > @@ -4102,11 +4102,11 @@ qcow2_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes) > return -ENOTSUP; > } > > - if (!QEMU_IS_ALIGNED(offset | bytes, s->cluster_size)) { > - assert(bytes < s->cluster_size); > + if (!QEMU_IS_ALIGNED(offset | bytes, bs->bl.pdiscard_alignment)) { > + assert(bytes < bs->bl.pdiscard_alignment); > /* Ignore partial clusters, except for the special case of the > * complete partial cluster at the end of an unaligned file */ > - if (!QEMU_IS_ALIGNED(offset, s->cluster_size) || > + if (!QEMU_IS_ALIGNED(offset, bs->bl.pdiscard_alignment) || > offset + bytes != bs->total_sectors * BDRV_SECTOR_SIZE) { > return -ENOTSUP; > } I've checked all the code paths, and as far as I see it nowhere breaks the discard_no_unref option. It's important that we don't introduce new code paths that can make holes in the qcow2 image when this option is enabled :) If you can confirm my conclusion, that would be great. Thanks Jean-Louis